Silicon-tapered waveguide for mode conversion in metal-insulator-metal waveguide-based plasmonic sensor for refractive index sensing.

In this study, we have undertaken a comprehensive numerical investigation of a refractive index sensor designed around a metal-insulator-metal (MIM) plasmonic waveguide. Our approach utilizes the finite element method to thoroughly analyze the sensor's performance. The sensor's configuration utilizes a ring resonator design, which has been slightly modified at the coupling segment. This modification enhances the efficiency of light coupling between a bus waveguide and the ring resonator, particularly at the resonance wavelength. This strategic adjustment significantly improves the device's extinction ratio, a critical factor in its functionality. Remarkably, the sensitivity of this sensor is determined to be approximately 1155.71 nm/RIU, while it possesses a figure of merit of 25.9. Furthermore, our study delves into the intricate mechanism governing the injection of light into the nanoscale MIM waveguide. We achieve this through the incorporation of silicon-tapered waveguides, which play a pivotal role in facilitating the transformation of a dielectric mode into a plasmonic mode, and vice versa. Ultimately, the findings of this research hold significant promise for advancing the field of plasmonic sensing systems based on MIM waveguide technology. The insights gained here pave the way for the practical realization and optimization of highly efficient and precise plasmonic sensors.

Plasmonic sensor based on metal-insulator-metal waveguide square ring cavity filled with functional material for the detection of CO2 gas.

In this work, a straightforward and highly sensitive design of a CO2 gas sensor is numerically investigated using the finite element method. The sensor is based on a plasmonic metal-insulator-metal (MIM) waveguide side coupled to a square ring cavity filled with polyhexamethylene biguanide (PHMB) functional material. The refractive index of the functional material changes when exposed to the CO2 and that change is linearly proportional to the concentration of the gas. The sensors based on surface plasmon polariton (SPP) waves are highly sensitive due to the strong interaction of the electromagnetic wave with the matter. By utilizing PHMB polymer in the MIM waveguide plasmonic sensor provides a platform that offers the highest sensitivity of 135.95 pm/ppm which cannot be obtained via optical sensors based on silicon photonics. The sensitivity reported in this work is ∼7 times higher than reported in the previous works. Therefore, we believe that the results presented in this paper are exceedingly beneficial for the realization of the sensors for the detection of toxic gases by employing different functional materials.

Ultrashort inverted tapered silicon ridge-to-slot waveguide coupler at 1.55 µm and 3.392 µm wavelength.

Herein, a compact and efficient inverted tapered ridge-to-slot waveguide coupler design based on the silicon-on-insulator platform is presented. The proposed device consists of three segments such as ridge waveguide, inverted taper segment, and slot waveguide. The coupling segment resembles a V shape, which provides good mode-matching between the ridge and slot waveguide. Two significant aspects of the proposed coupler design are discussed. In the first part of the paper, the coupler design optimized at 1.55 µm is suggested for optical interconnect. The propagation loss and coupling efficiency of 1.69 dB/µm and 91% are obtained for the 100 nm long tapered segment introduced between the ridge waveguide and slot waveguide, respectively. This propagation loss of the device includes the loss suffered by the ridge waveguide, tapered segment, and slot waveguide. Our proposed device design can be used in integrated optical platforms, where the efficient coupling of light to slot waveguides is required. Whereas, in the second part, the coupler design is optimized at the mid-infrared of 3.392 µm for an evanescent field absorption methane gas sensor. Slot waveguide offers excessive light-matter interaction due to its strong mode confinement in the low index material. The evanescent field ratio of ∼0.73 is obtained for the optimized waveguide geometry. As a result, 3 dB decay in the transmitted power can be obtained at 60% of gas concentration present in the ambient medium.

Design of mirrors for generating prescribed continuous illuminance distributions on the basis of the supporting quadric method.

A method for the design of reflecting surfaces generating prescribed continuous illuminance distributions in two-dimensional domains is proposed. The mirror surface is represented as an envelope of a two-parameter family of ellipsoids. The first focus of each ellipsoid coincides with the point light source, while the second one is located at the illuminated domain. This surface representation can be interpreted as a limiting case of a segmented surface used in the supporting quadric method for focusing onto a set of points. The envelope equation depends on the function defining the lengths of the major axes of the ellipsoids of the family. The calculation of this function is performed using a continuous approximation of a discrete function obtained from the solution of a discrete problem of focusing onto a set of points. High efficiency of the proposed method is illustrated by the designed examples of mirrors for generating uniform illuminance distributions in areas of different shapes.

Design and investigation of color separation diffraction gratings.

Color separation gratings (CSGs) are designed within the framework of the rigorous electromagnetic theory using a gradient method. The optimality of the scalar-theory-based solutions is estimated. The results of the experimental study of a CSG to separate three wavelengths are presented.